The invention relates to a method for operating an internal combustion engine, especially of a motor vehicle, by means of a control apparatus wherein a number of functions are carried out at time intervals and/or in dependence upon the rpm of the engine and wherein a quantity is determined which defines the utilization or work load of the control apparatus and wherein a quantity is determined defining the rpm of the engine. Furthermore, the invention relates to an internal combustion engine, especially for a motor vehicle, having a control apparatus by which a number of functions can be executed at time intervals and by which a quantity, which defines the utilization of the control apparatus, and a quantity, which defines the rpm of the engine, can be determined.
For the open-loop control and/or closed-loop control of modern engines, especially of motor vehicles, it is necessary that a number of functions be executed by a control apparatus, especially by a microprocessor. Accordingly, it is required, on the one hand, that so-called basic functions, such as the mass of the fuel which is to be injected into the combustion chamber of the engine or the time point of the ignition of the injected fuel mass are determined in dependence upon the rpm of the engine. These functions are thereby in synchronism with the rpm. On the other hand, there are functions such as adaptation functions which must be executed by the control apparatus at pregiven time intervals. Such intervals can, for example, be a raster of 10 ms or the like. These functions are thereby time-synchronous.
With a high rpm of the engine, the rpm-synchronous functions must be executed significantly more frequently than at a low rpm. If, for a high rpm of this kind, a plurality of time-synchronous functions is added which must be computed by the control apparatus, then it is possible that the control apparatus is overloaded. This can lead to malfunctions of the control apparatus.
To avoid such malfunctions, it is provided that a quantity is generated which defines the utilization of the control apparatus. This quantity can be applied to prevent possible overloads of the control apparatus.
Proceeding from the above, it is an object of the invention to provide a method for operating an internal combustion engine, especially of a motor vehicle, which includes measures which counter an overloading of the control apparatus.
This object is solved in a method and/or in an internal combustion engine of the above-mentioned type in accordance with the invention in that the number of executed functions is reduced when the quantity, which defines the utilization, is greater than a utilization threshold value and/or that the time intervals of the execution of the functions is increased when the quantity, which defines the rpm, is greater than an rpm threshold value or when the quantity, which defines the utilization, is greater than the utilization threshold value.
An overloading of the control apparatus is countered by the reduction of the number of the executed functions and/or the increase of the time interval of the execution of the functions. If, for example, the quantity, which defines the utilization of the control apparatus, shows that the control apparatus is almost overloaded or is already overloaded, then, and according to the invention, the number of the executed functions is reduced with the consequence that the control apparatus must execute fewer functions and thereby is less loaded. The threatened overload of the control apparatus and/or the already occurring overload of the control apparatus is countered in this way. According to the invention, the time interval of the execution of the functions is increased when the quantity, which defines the rpm of the engine, and/or the quantity, which defines the utilization, indicate that especially the above-mentioned basic functions must be carried out very often because of a high rpm and that therefore an overload of the computing apparatus is possible. This has the consequence that the above-mentioned functions no longer have to be executed so frequently and that the control apparatus is thereby relieved. An overloading of the control apparatus is therefore also countered in this way.
In total, with the measures of the invention, it is prevented that the control apparatus is overloaded. The risk that faults occur because of overloading is thereby significantly reduced. The invention thereby contributes to the correct and reliable operation of the engine.
In an advantageous embodiment of the invention, the number of functions is subdivided into classes having different priorities and those functions having the lowest priority are not executed when the quantity, which defines the utilization, is greater than the utilization threshold value. In this way, it is achieved that first those functions are not executed which have only a lesser significance for the operation of the engine. In this way, it is guaranteed that the functions, which are essential for the operation of the engine, are at least not immediately switched off. The correct and reliable operation of the engine is thereby ensured even after a switchoff of functions.
In a further advantageous embodiment of the invention, an additional threshold value is provided which is less than or equal to the utilization threshold value and the functions having the second lowest priority are not executed when the quantity, which defines the utilization, is greater than the additional threshold value. In this way, it is achieved that (when the switchoff of the functions having the lowest priority is still not sufficient to prevent an overloading of the control apparatus) those functions are additionally switched off which are provided with the second lowest priority. This defines, in total, a stepwise switchoff of the functions. At each step, always the functions having the respective lowest priorities are no longer executed. In this way, it is ensured that the functions, which are essential for the operation of the engine, are only switched off very late. The correct and reliable operation of the engine is in this way substantially maintained even for a large overload of the control apparatus.
It is especially purposeful when the following functions are provided wherein the sequence of the functions corresponds to their priority: basic functions such as injection, ignition; engine protective functions such as knock control; exhaust-gas functions such as lambda control; comfort functions such as load impact damping; diagnostic functions such as detection of misfires; adaptation functions such as adaptation to vehicle scattering. Because of the high priority, of, for example, the exhaust-gas functions, it is ensured that the probability for the switchoff of these functions is very slight. It is understood that the breakdown into functions of this kind, and also the allocation of priorities to functions of this kind, can also be arranged in a different way.
In an advantageous configuration of the invention, at least some of the functions, for example, basic functions, are completely executed in each case. This means that the basic functions cannot be switched off. In this way, it is achieved that the engine remains operable in each case. For an advantageous further embodiment of the invention, at least some of the functions, such as the exhaust-gas function, are broken down into component functions and only one or several of the component functions are not executed. For example, it is possible that also for a utilization of the control apparatus at which the exhaust-gas functions must have actually been switched off, these exhaust-gas functions are not completely switched off; instead, at least basic component functions of the exhaust-gas functions continue to be executed. In this way, it is ensured that even for an overload of the control apparatus (for example, statutory exhaust-gas determinations which are realized via the exhaust-gas functions) are in each case maintained.
In another advantageous embodiment of the invention, the time interval of the execution of the functions with the rpm of the engine and/or the utilization of the control apparatus is linearly or stepwise increased when the quantity, which defines the rpm, is greater than the rpm threshold value and the quantity, which defines the overload, is greater than the utilization threshold value. In this way, it is achieved that the time interval of the execution of the functions becomes greater, for example, with increasing rpm. A linear relationship can be present between this time interval and the rpm or the increase of the time interval takes place in one or in several jumps. In each case, with the procedure described, an overload of the control apparatus is countered so that a correct and reliable operation of the control apparatus is achieved. The same applies to an increasing utilization of the control apparatus.
In a further advantageous embodiment of the invention, an additional threshold value is provided which is greater than the rpm threshold value and/or the utilization threshold value and the time interval of the execution of the functions is maintained constant when the quantity, which defines the rpm, and/or the quantity which defines the utilization, is greater than the additional threshold value. This means that after the additional value is exceeded, the time interval of the execution of the functions is not increased further, instead, it remains constant.
In an advantageous embodiment of the invention, the time interval of the execution is increased only for those functions which are not dependent upon the rpm of the engine, that is, not for basic functions, for example. In this way, it is ensured that, for example, the basic functions are executed in each case in the time raster required for them. For example, in the basic functions, the time interval of the execution is not changed even for a high utilization of the control apparatus. In this way, it is ensured that even for a high utilization of the control apparatus, the basic functions are correctly and reliably executed and thereby the operation of the engine is maintained in each case.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an engine especially of a motor vehicle. A program is stored on the control element which is capable of being run on a computing apparatus such as a microprocessor and is suitable for executing the method of the invention. In this way, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for which execution the program is suitable. As a control element, especially an electric storage medium can be applied, for example, a read-only-memory.
Additional features, application possibilities, and advantages of the invention become evident from the description of the embodiments of the invention which follows and which are shown in the figures of the drawing. All described and illustrated features define the subject matter of the invention by themselves or in any desired combination independently of their summary in the patent claims or their dependency as well as independently of their formulation and/or illustration in the description and/or in the drawing.